H4 magneto help

HighSierra86

New User
Hi guys, I have a no-fire condition on an H4 magneto. Tractor is a 45' H that I rescued last summer. Been sitting for 30 years. Came with a new, (rebuilt) magneto that had never been installed. The mag has been sitting in a box on its side since at least 1993.

I installed and timed the magneto with no luck. The timing went fine but I have no spark at all. Replaced and adjusted points and condenser. I replaced the coil also as it seemed to me to be grounding out on the wire to the cond. New coil tests exactly the same, close to 0 ohms from primary wire to grounding strap. I don't have the blue ribbon manual, but I was told this is normal? .5 ohms to ground? Top button to wire measures 11.5 ohms.

I have verified no shorts between the cond and points with the coil disconnected.

Is there something I'm missing? only odd thing I noticed was an oil-like residue that had seeped out of the main shaft on the points side of the mag. Something from sitting on its side for so long? Or maybe some kind of assembly lube, seeing as it was rebuilt.

And hints or tips would be greatly appreciated. I'm loosing sleep trying to figure this one out! Thanks in advance, Nick.[/img]
 
An almost zero ohm on primary is normal and about 7000 ohms on primary of coil. Be sure points are set to .013. You might even want to unhook coil primary wire from points and then check to see that with points closed you have zero ohms and with open points you have infinity. Have seen many where that condenser lead is turned wrong and grounding out, especially when installing the screwed on reduction plate it ground them out. Also, be sure to check for spark before putting it on the tractor. Lot simpler that way turning it over by hand.
 

Thank you for the replies.

I have verified the readings you described for the points. The readings become difficult after hooking up the coil, as it reads so close to zero ohms...in any other system i would think something is grounding out. My points are brand new and set for .013

I should be able to see the spark jump the points with the covers removed correct?? I have test fit everything back together still with no spark either way.

Teddy52food....I am located in CT. Thank you for the offer, I am stubborn in always trying to fix everything myself. Even though i realize its sometimes better left up to the experts!

Thanks again for any additional ideas/troubleshooting, Nick
 
You do not want spark to jump the points. That is wasted energy that is jumping because the secondary coil winding cannot find a place to express it's built up voltage. You always check for spark at the coil output terminal. With top cover on the magneto, just plug a wire in there and hold other end close to magneto frame, anyplace. With cover off, just tough one end of wire to output terminal of coil. High voltage spark plug type wire of curse. When that impulse snaps you should get a nice fat spark. You could hook a wire to a spark plug if you are not comfortable holding onto the wire but ground that plug exterior to magneto frame. I usually take an old plug and cut the external electrode off so spark has to jump a nice size gap as it should .

On another note. Leaving any high tension coil wire open circuited, (like pulling the wire off a spark plug and just leaving it lay away from a ground) is the most common way to ruin a coil. That is really tough on coils like in lawn mower. People unhook wire, forget it , pull and pull no start, ruin coil. That voltage is trying it's darndest to go some place and it will penetrate the internal insulations.
 
(quoted from post at 11:46:02 04/20/18) You do not want spark to jump the points. That is wasted energy that is jumping because the secondary coil winding cannot find a place to express it's built up voltage. You always check for spark at the coil output terminal. With top cover on the magneto, just plug a wire in there and hold other end close to magneto frame, anyplace. With cover off, just tough one end of wire to output terminal of coil. High voltage spark plug type wire of curse. When that impulse snaps you should get a nice fat spark. You could hook a wire to a spark plug if you are not comfortable holding onto the wire but ground that plug exterior to magneto frame. I usually take an old plug and cut the external electrode off so spark has to jump a nice size gap as it should .

On another note. Leaving any high tension coil wire open circuited, (like pulling the wire off a spark plug and just leaving it lay away from a ground) is the most common way to ruin a coil. That is really tough on coils like in lawn mower. People unhook wire, forget it , pull and pull no start, ruin coil. That voltage is trying it's darndest to go some place and it will penetrate the internal insulations.

I've never really thought about the reasoning behind spark jumping the points...that makes sense, especially in regards to possible coil damage. Thank you for the tip.

For those who may find this post at a later date with the same problem, I did solve the problem, however I'm not sure of exactly what the solution was.

I first installed a missing brass washer on the screw for the stationary point base (cnh part no.21394D). I also noticed while tightening the outer lug for the kill switch on the side of the mag, the internal wire terminal for the cond. would spin and come very close to touching the magneto case..a very possible source for grounding. I double checked all my clearances again and re-assembled the mag. I finally had a nice fat blue spark off the coil wire to ground, and in turn, spark to all the plugs.

Tractor runs beautiful after a 30+ year nap! Thank you for the replies. -Nick
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top